Knife sharpening device



C. L. JENKS KNIFE SHARPENING DEVICE fji 11,

Filed April l. 1957 3 Sheets-Sheet 1 June 1l, 1940. c. L. JENKs KNIFE SHAEFENING` DEVICE Filed April 1. 1937 s sheets-sheet 2 v JUN 11, 1940- c. l.. JENKsl 2,203,788

' KNIFE SHARPENING DEVICE .i

Filed April l1. 1957 :s sheets-sheet a Patented June 11,1940

UNITED STATES PATENT ol-Flcs t 2.2mm

j @.NEJR EM Application Apl'll 1, 193?, Sel'ill N0. 134,289

8 Claims.

This invention relates to a device for sharpening knives, and especially to an abrasive wheel having a surface of revolution so shaped and.-

used that it will sharpen various types of edged o tools or cutlery, such as household knives, to a predetermined bevel. t

` Knives of the standard shapeare ordinarily sharpened either on a `fiat surfaced abrasive stone or by means of a cylindrical grinding wheel, rotated either by power or by hand. which is so arranged that the knife edge may present an extensive line contact with the wheel face. To sharpen the knife on such devices, it has been necessary for the operator to exercise consider- 16 able skill in holding the knife at the correct angle `to produce a satisfactory bevel. and to main tain `the knife always at that same angle whileV it is moved back and forth across the wheel face. This requirement has made it difficult for the "20 average person to keep household and other knives in a satisfactory condition. `To overcome such diiliculties, various devices have been proposed for use with the cylindrical abrasive wheel, which are intended to hold the knife at a suitable angle, but their adjustment and use as the wheel wears awayhas presented further problems which have rendered them impractical for Vuse in the average hme. Various other types of knife sharpening devices have been marketed for household use, yet they either do not possess satisfactory abrasive characteristics or are based on incorrect principles which do not permit a `knife edge to be sharpened to a proper shape and a desired neness of edge.

The primary object of this invention is to provide a knife sharpening wheel whose effective abrasive surface is so shaped thatit is capable of sharpening a knife edge to a predetermined bevel without the exercise of skill or more than ordinary care on the part of the operator, and which' is particularly adapted for `use in the home.

A further object is to provide a knife sharpening device inwhich a specially` shaped abrasive stone is so arranged forrotation, either by power or by hand, that the device may be easily mounted in a convenient location and a knife may be sharpened thereon with the minimum of mechanical effortand skill. A further object of the invention is to provide a device for sharpening knives which serves with a special shape of rotating grinding wheel to produce a satisfactory knife edge of a predetermined and invariable bevel without requiring that the user` follow more than ja simple principle of operation. Further objects will be apparent in the following disclosure. l

In accordance with this invention, I propose to make a knife sharpening abrasive wheel of a special shape, herein termed a concave conoid, and to hold the knife against its'peripheral surface in such a position, with both its sharp edge and its back edge touching the wheel, that the knife ,edge will be ground only to that bevel which is predetermined by the 'wheel shape. 'Ihis abrasive wheel or stone is preferably so shaped that the beveled edge of the knife may touch the wheel only with a pointcontact as it is moved 1ongi tudinally in substantially parallel planes back and forth across any portion of the rotating abrasive surface. This specially shaped wheel` may be mounted in various constructionalA arrangements on a vertical or a horizontal axis or otherwise as desired, and the wheel may be rotated either by hand or by power and at a suitable `speed for a knife sharpening operation.

Referring to the'drawings illustrating various embodiments of the invention;

Fig. 1 is a perspective view, with parts broken away, of one shape 'of abrasive wheel on its ispindle mount and showing the correct manner of holding a knife for sharpening it;

Fig. 2 is a diametrical sectional view of the Wheel of Fig. 1 which illustrates the principle of operation of the concave conoidal shape of the wheel;

Figs. 3, 4, 5, 6 and rl show diametrical sectional views of `various wheels which embody the shape of a concaveconoid:

Fig. 8 is a. perspective view of a wheel of a lfncuve conoidal shape similar to that shown in Fig. 9 is an enlarged section of a knife blade showing theshape generated by the wheel;

Fig. 10 is a vertical elevation, partly broken away and partly in section, showing an electrically driven motor directly connected for rotating the concave conoid stone;

Fig. 11 is a fragmentary sectional view showing an abrasive stone and its spindle adapted to be removably mounted on associated driving parts of a power operated household device;

Fig. 12 shows a similar fragmentary sectional view of a stone anda removable spindle which "serve to mount the stone on another type of power driven apparatus;

Fig. 13 `shows in vertical section, partly in eleternal of the circle; and this axis may coincide Fig. 14 is a fragmentary perspective view of the frame of the device of Fig. 13;

Fig. 15 is a sectional view of another shape of wheel adapted for use on either a hand operated or a power driven machine; and

Fig. 16 is a vertical sectional view of a device having the stone mounted on a base for rotation by the frictional drag of the knife.

In accordance with this invention, the abrasive Wheel or stone I has an abrasive surface of revolution II so shaped that the blade I2 of the knife may be held with its sharp edge I3 and 'its back edge I4 (Figs. 1, 2 and 9) in contact with the rotating surface and the knife edge I3 will be automatically sharpened to a predeter- `mined bevel, when the wheel is revolved by means of its spindle I5 and the knife is moved lengthwise of itself back and forth across the wheel.

The shape of the abrasive wheel is developed,

With or be parallel to a line I8--YI8 tangential to or intersecting the curve I6 adjacent to one end thereof. This surface is herein termed a concave conoid, and this term is to be construed as covering both the geometrical figure, such as is shown in Fig. 3, and the frustum thereof, such as is illustrated in other figures of the drawings. In the construction of Fig. 3, the axis of rotation coincides with aline I8-I8 which is substantially tangent to one end of the curve I6, but the apex of the conoid is preferably rounded or thickened for the sake of safety, as is indicated in Fig. 10. A

The line I8-I8 may also be tangential to the curve I6 at an intermediate point, such as its center, in which case, as shown in Fig. 4, a spool shaped body I 9' is thereby developed, which is especially adapted for certain types of knife sharpening operations, where the stone is so constructed that a knife may be held with its back edge against the slower moving central portion of the'wheel and either side of its sharp edge against the faster portion. 'I'he shape may also take that shown in Fig. 5, which oiers an advantage in that both sides of a knife may be sharpened without reversing it end for end,

- where the stone is mounted on a horizontal axis.

In this construction, the two abrasive portions are generated by the revolution of two arcs of circles I6v about the axis of the wheel I0 and its spindle 2l. It will be appreciated that the constructions of Figs. 4 and 5 may be viewed as made up of two bodies of the Fig. 2 construction placed end to end; but all of the various shapes herein described are to be considered as embracediwithin the term concave conoid. l

If, as shown diagrammatically in Fig. 2,'a knife blade I 2 is held with its sharp edge I3 and its back edge I4 resting against the concave conoid portion of the abrasive wheel or stone III, while the knife is held in the general position illustrated in Fig. 1, or with its edge cutting at right angles a diametrical plane through the wheel axis, then upon rotating the stone about its axis the knife edge to be sharpened will be ground thereby and take the convex shape determined by the corresponding concave arc I6 of the stone. By moving the knife back and forth across the rotating stone in the direction indicated by the double arrow in Fig. 1, its edge will then be shaped to that particular curve. The knife may be reversed end for end, or the knife edge held against the opposite side of the stone, in order that the other side of the blade may be given a similiarly shaped surface. f It is preferable that the blade edge be so located as to be sharpened on the base portion of the conoid with the back of the knife on the apex which has the lower surface velocity and lesser abrading ability.

Itwill be noted by reference to Figs. 2 and 9 that the points I3 and I4 on the knife blade, taken with another point 25 representing the back edge of the bevel (shown in exaggerated size) form three points of a triangle; and these three points are capable of lying always within any portion of the circle determined by the radius of the curve I6. Hence, it is immaterial where the knife blade is held on the stone, as indicated diagrammatically in Fig. 2 .which shows a second position for the knife in dotted outline. Just so long as the knife is moved back and forth across the rotating stone substantially parallel with the direction indicated in Fig. 1, then this knife edge may ride up and down the stone and the convexity and the width of the bevel thereof, i. e. the distance between the points I3 yand 25 in Fig. 9, will be determined solely by the radius of the generating curve I6 of the stone. Hence, the operator need not use any particular skill in holding the knife against the wheel, except that he should move the knife continuously and preferably uniformly to prevent grinding scallops in the blade and to secure good results.

It will be particularly observed, as shown in Fig. 9, that the knife is not hollow ground but that its bevel is slightly convex, the degreeof which depends on the radius of theV generating curveA I6`. A hollow ground knife has -a wide edge portion of extreme thinness where the two'` opposite concave surfaces meet and the material of the knife blade at vthis point is necessarily weak and fragile. As is commonly known, a razor blade tends to break with microscopic cracks extending along its edge and thus to form teeth which bend to the opposite sides and so produce a ragged blade edge, which must be stropped to bend the teeth back into alignment.' A knife sharpened on a concave conoid surface as here described will, on the contrary, be thick and strong close to the sharpened edge, and yit will not readily crack and bend laterally to form .ragged teeth.

Various combinations of this shape of wheel may be made with other shapes. For example, as shown in Figs. 6 and 8, the concave conoid surface generated by the are of a circle 21 may be merged into acylindrical surface 28, or a cylindrical surface 29 may be combined with the conoid wheel for use in ordinary operations. In these figures, all three forms are combined. Also,

' by combining two of these constructions end toend, as shown in Figs. -4 .and 5, still further shapes are formed. lLikewise, the flat ends of the wheels may be serviceably employed in grinding knives or other implements, and particularly in touching up the edge on a fine oil stone type of surface after the bevel has been shaped by the concave conoid surface. Stones wheel.

l aaoavss particularly adapted forthis purpose are shown indicated by the portion 32.` But ordinarily, only one of these surfaces 3| or `32 will be formed `on y the4 stone. `The curve 3l is located in a position of low surface velocity and` is best suited for a careful slow motion finishing operation. With this wheel, the knife may be sharpened initially on'the portion 30, and then for a finishing operation it may be moved towards the apex porf tion 3i or the lbase portion 32 so that its edge contacts with that surface of lesser radius of curvature. This serves to round the beveled portion of the knife and to superimpose ashort radius bevel on the other long radius bevel at the knife edge, and thus to eliminate any burr, raggedness or other type of imperfection that may have accidentally "crept in,iand to sharpen the blade still better. These portions 3i and 32 may also be made of finer grains or of a different structure fromthat of` the other part of the i The radius of curvature of the` arc I6 may vary widely depending upon the` widthof 'the bevel desired, but I have `found that a radius of from l to 4 inches, and preferably in the range of 11A to 2*/2 or 3 inches, is satisfactory for grinding the standard types of knives. A short radius gives `an abrupt bevel and a long radius a more. gradual taper.

The radius of curvature will be determined in part bythe widthof the `knife blade, i. e. the distance between the front and back edges I3 and I4, and ordinarily a wider blade will take a larger radius of curvature. The stone may be made as a compromise for various Vtypes of knives, and I have found that `a radius of about 2` inches is satisfactory for the knives most commonly used in the household. For `the average requirements the curvatures indicated in the drawings may be considered as drawn to a full y scale. y

r `The wheel size may be made as large as desired, since the size has no effect on the grinding operation except that of `varying the peripheral speed `of the conoid surface. A manufacturer of cutlery may use a` wheel o f the shape of Figs. l, 2 and 13 and make it of any desired large diameter so that it may be repeatedly trued as it wears away and thus provide a long life of service. However, for ordinary householduse, the

wheel is preferably made quite small, and therefore, inexpensive. A wheelof small diameter will permit grinding a knife blade much closer tothe handle 34 (Fig. 1) which tends to strike the `wheel before `the heel35 of the blade has cloth, or in making what is known as a set-up wheel. It is, however, preferred that the abrasive wheel comprise a` solid body of bonded abrasive grains, such' as crystalline alumina, corundum, silicon carbide and boron carbide, or

theinferior abrasives of the type ofemery, quartz `For a very cheap construction, a conoid i and garnet. These grains arebonded with standard abrasive bonds, such as vitrifled. ceramic materials, vulcanized rubber, sodium silicate, shellac or various potentially reactive, heat settable resinoids of the general type of a phenolic formaldehyde condensation Vproduct or `a `phthalic glycerol` resin.

The standard procedure for making such. articles `comprisesmixing the abrasive grains of required sizes with the raw bond in suitable proportions, and thereafter setting the bond by means of heat. The concave conoid shape `may be formedieither before or after the bond is set by heat; but if the-bond is a resinoid or rubber, this is `preferably accomplished by moldingthe raw mixture of abrasive and bond in a properly shaped mold prior tothe heat setting operation. If required, the article may be further shaped by` a truing operation prior to.,or after it` has been made or put into use. If the wheel is made of a vitrified ceramic bond, the mixture of grains and raw bond may likewise be shaped in a mold under pressure before Athe wheel is fired to vitrify the bond. The vitrifled wheel may also be shaped by truing the fired article. Various standard procedures may be used in the manufacture of the wheel, as is well understood by those skilled in the art.

It is found that in the ordinary use of the stone, the knife edge tends to dress or true the abrasive body to a correct shape and thus to renew its abrasive qualities. This truing tendency is due to the fact that the knife edge contacts with the Wheel only at a substantially point contact and it is not always moved properly parallel to itself during the sharpening operation. It is,

therefore, desirable to employ an abrasive grain A satisfactory wheel for the purpose of sharpening knives may be made of crystalline alumina or silicon carbide abrasive of a grit size of 400 to 600 meshes per linear inch and particularly, that abrasive size which is known as `in the trade. Such an abrasive is preferably bonded by means of a vitried ceramic material proportioned to give a grade of about N to P and an open, highly porous structure of 10 to 12 on the Norton scales of hardness and structure.

The resinoid and rubbex` bonds are also particularly serviceable for the purpose, and the grain sizes and grades of hardness for these bonds may be the same as above specified. These wheels may be used like a slow motion oil stone wheel or at'speeds much lower than recommended for grinding knives on ordinary cylindrical wheels; and I have found it desirable to run the wheel at a comparatively slow rate for a ne finishing operation, such as 200 to 1000 surface feet per minute or slower.

The back edge of the knife-necessarily rests on the surface of the abrasive wheel and so may become abraded to some extent. But, if the knife is so placed that its sharp blade edge is adjacent to that portion of the surface of the higher rate of peripheral speed, then the back edge will vlie against a slower moving portion of the wheel and will not be ground to any serious extent; vand it will be unnecessary yto -take any precautions where ordinary kitchen knives are concerned. If it is desired to avoid grinding the back edge i4 (Fig. 9) of the knife, then thatportion 38 of the conoid surface (Figs. 3 and 10) which will normally contact only with the back edge Il may be made of a non-abrasive and comparatively smooth material, such as a synthetic resinoid, rubber, wood or the like. If desired, thewheel may be made as a one-piece structure of bonded abrasive, such as abrasive grains united by vitriiled ceramic material, after which the apex 36, or the base portion if desired, may have its surface iilled with a non-abrasive material, such as rubber, a natural resin or a synthetic resinoid, and thus provide a comparatively smooth surface.

If the wheel is made of resinoid bonded abrasive, then the non-abrasive material may be a resinoid molded to form the apex portion 38 at the timewhen the abrasive body is shaped, and the resinoids of the two portions may be heat set and united integrally at the same time. Similarly, a rubber bonded abrasive wheel may be provided with a, vulcanized rubber apex by molding a non-abrasive rubber apex and the abrasive and rubber base portion at the same time and If the wheel is made of abrasive grains bonded with vitriied material, then rubber or resinoid or other non-abrasive material may be molded onto the end of the abrasive portion after the vitrifying operation and then be heat treated to set it to a hard body.

The junction of the two portions may be effected by impregnating the pores of the vitriied body with liquid resinoid, such as Bakelite phenolic aldehyde resinoid in the unconverted stage, after which the body portion 36 is molded in contact with the impregnated surface by the use of a resinoid molding compound, such as a mixture of dry and liquid resinoid together with Asuitable llers of wood powder, clay, pulverized minerals, or other appropriate material. Other resinoids, such as the glycerol resins, may also be used. Standard methods well known in the abrasive industry may be used for the purpose. Likewise, a vulcanized rubber tipmay be formed on a vitrified stone, by pressing a compound of raw rubber, sulfur or vulcanizer into the surface pores of the abrasive body and shaping the apex 36,

after which the body is heated to vulcanize the rubber. The `sulfur content will be proportioned as required to-make either a soft rubber or a hard rubber. It is also feasible to mount the knife in edge of the knife but leaves the blade edge exposed.

'I'he abrasive wheel may be mounted on its driving spindle in numerous ways, such as by the nuts I0 shown in Fig. 5, which have right and left hand threads and serve to clamp the wheel therebetween. As indicated in Figs. .1, 2 and 8, the wheel may be provided with a central hole enlarged at one or both ends to receive a metal washer 4I tted against a shoulder on the spindle and lock nuts 42 adapted to secure the wheel in place. If desired, the wheel hole may `be provided with alead or other bushing, as is standard practice for some types of wheels, which lits .the spindle accurately. A1so,`as shown in Figs.

3 and 'l a nut 43 may be suitably cemented, as by means of melted lead or sulfur, in a recess in the large end of the conoid and this nut may be threaded internally to receive the end of a threaded spindle. If the wheel is made of a low temperature molding compound, such as'is the aaoavss case when the abrasive is bonded with rubber or a resinoid, a metal nut M may be embedded in the molded body, as shown in Fig. 10; or the bond may be itself molded or tapped to provide a threaded surface, as shown in Fig. 15. Like-V wise, a metal bushing, such as Babbitt metal, may be cast to form a threaded surface, as indicated in Fig. 13.

One feature of this construction is the feasibility of usinga vertical spindle and so mounting the sharpening stone that the two sides ofthe knife blade may besharpened by merely moving the knife from one side of the stone to the other. In that case, the stone is preferably so mounted that the apex of the conoid extends upwardly so as to permit the knife blade to be held with the same degree of pressure under the iniiuence of gravity against both sides of the stone with its edge extending downwardly, as shown in Figs. 1, 10 and 11. The constructions of Figs. 4, 5 and 6 are intended especially for mounting on horlzontal axes. 'I'he axis may, however be arranged at any angle relative to a horizontal line.

Moreover, due to the feasibility of using a stone of very small diameter, it is possible to drive the wheel by a 'direct connection with an electric motor spindle and so at the same revolutions per minute, and thus provide a compact and com-- paratively inexpensivel apparatus. A construction of this type is shown in Fig. 10, which comprises an electric motor 50 of suitable construction arranged to take either a direct or an alternating current, or both. The motor should have an end thrust bearing at one end of the spindle 5| and a radial thrust bearing at each end which will serve to take the thrusts set up during use of the device. This is diagrammatically i1- lustrated in the drawing, wherein the armature spindle 52 has its upper end threaded for connection with the nut 44 embedded in the abrasive stone. An enlarged flange 53 on the spindle 52 `rests on a suitable ball bearing 54, which is adapted to take both the radial and the vertical thrusts and may b e of anyk desired construction for that purpose. These ball bearings are held in place by the flange 55 on the upper end of the casing.v Likewise, a flange Si on the bottom of the motor casing serves to hold in place the radial ball bearings 51 which hold the lower end of the motor spindle. 'I'he construction of the electric motor may be as desired for the purpose of rotating and supporting the abrasive wheel.

The motor casing may be provided 'with a metal base plate 5I arranged for supporting the same in a vertical position. If desired, this base plate may be provided with spaced rubber buttons or preferably a sheet 59of soft rubber vulcanized or cemented to its under surface so as to provide a frictional support that will not permit the device to creep during use. Any of the stones herein described may be used on this spindle. The rotational speed may be as desired, such as from 200 to 1800 R. P. M., depending on the size of the stone and the u'se to which it is to be put. For the sizes of wheels herein described, this gives an eifective surface speed at the line of contact with the knife edge which is no more than the numerical value of the R. P. M. For example, the corresponding surface speeds would be about 100 to 900 S. F. P. M. for the wheel of Fig. 10. By means of a suitable resistance provided for the purpose, the speed may be regulated as desired. Y

'I'he arrangements shown in Figs. 11 and 12 are especially adapted for use on the multi-D11rD0ae Ithe spindle 63 may thedriven spindle. For the purposes of grinding knives thereon, I have provideda special fitting so that one may remove the standard porcelain or metal body used for extracting orange juice and substitute an abrasive wheel therefor. The arrangement of Fig. 11 is adapted for use on that type of machine which comprises a rotatable shaft having a hollow sleeve like end 69 and a driving pin 6i adapted to engage the slotted end 62 in the short spindle63 secured to the stone 64. Y The spindle 63 may have an enlarged head 65` cemented in the stone, or it may be secured thereto by any of the above described methods, such as by being removably threaded into a Babbitt bushing cast in a recess in' the base portion `of the stone. `The driving shaft, driven-by an electric motor, has a` suitable speed for the stones of a the shapes, and `dimensions shown in the drawings.` L

.TheFig; 12 construction is adapted foruse where .the spindle 68 oi the juice extractor remains on the machine and has a hexagonal or other shaped head 69 on its exposed end which removably tsin a sleeve formed or cemented in the wheel .1L The spindle 68 is suitably driven by a slot and tongue connection with-a power driven shaft 12 in the machine. In this construction, the short spindle 68 ordinarily-re mains in place and the wheel 1I is removed therefrom, when the machine is to be used for other purposes; while in the Fig. 11 construction. remain fixed to the stone if desired. i

` As shown in` Fig.`13, the abrasive stone 8,0 may be provided with a large plane face 9| which l may serve for a ilnal iinishingoperation on a knife 'after the bevel has been formed by means of the concave conoid fac'e 82. 'Ihis type of wheel is particularly useful because the face 8l has the qualities of a slow speed oil stone and is adapted formany sharpening operations.

` 'I'he stone, for use on either the handoperated or the power` driven devices, may alsobel pro- )vided with a spindle mounting as shown in Fig.

15. In this arrangement, the wheel is adapted for mounting with either the base or the apex at l the top. To this end, the stone is provided with screwthreads in bothuthe apex and the base `for mounting on the threaded spindles. This may be simply done, if the wheel is made of a molded resinoid or rubber bond intermixed with the abrasive, by forming an axial hole 83 through `the `wheel and providing threads at the ends thereof. 'I'his construction permits one to sharpen a knife on the concave conoid surface 82,

and thus produce the right bevel, if the wheel is mounted, preferably, with the fiat base at the bottom. By turning the wheel over and mounting it in the position shown in Fig. 15,`the top f flat surface 8| is then available for use as an oil stone to sharpen all `sorts of implements or to touch' up a knife. edge previously beveled on the concave conoid portion of the stone. The stone may, if desired, be usedpermanently in the position shown in the drawing, since it isfeasible to hold the knife against the .under side conoid surface with the blade edge upwards.

As shown in Figs. 13 and 14, a hand operated `device may be one in which a handle is connected to the stone through an intermediate set of gears which serve to increase the speed of the stone; but if desired the handle may be directly conthereto so that by means of the thumb screw 86 threaded through the lower flanged member 81 the device may be mounted on the edge of a table. The short downwardly depending leg 88 of the upper U-shapedportion of the frame is provided with a bearing hole 89, and a similar hole 9U is provided in the long leg vso that a hand operated spindle 92 may be suitably mounted in these bearing holes for rotation about a horizontal axis. rIjhis spindle 92 is bent, as shown, and a handle 93 on its end serves to rotate it. A large driving gear 95 is suitably secured to the spindle 92 as by means of a pin, and it is arranged to mesh with and drive a small bevel gear 96 which serves to rotate the abrasive wheel.

99 rests on the top of the hub 99 and serves as an end thrust bearing. The upper end of the wheel shaft 9B is threaded and the wheel 80 is provided with a threaded bushing |02 adapted for removably mountingl the wheel on the shaft. Various other forms of mounting may, of course, be used.

The small bevel gear 9B is secured to the lower end of the shaft 98 by means of a collar N3, and a cotter pin or other suitable means `may be provided for holding the gear upon the shaft. Washers |04 and |05 together with a cotter pin I 06 serve to locate the driving spindle 92 with its bevel gear 95 in mesh. with the driven gear 96. `Protective covers may be added to prevent contact with the gears, and the construction may be suitably modified as required to give the proper speed to the grinding wheel, and it being understood that the illustrated embodiment is simply for the purpose of indicating one preferred form tatably fits on a vertically projecting spindle'or pin I i4 formed integrally with or secured to a Afiat base plate i I5. It is preferred that the parts be so shaped that the stone will not contact with the fiat base plate but will merely frictionally engage the Babbitt metal bushing. 'I'he friction between these parts should be such that when a knife is drawn horizontally across the stone, the tendency for the stone to rotate is restrained and the stone will turn only to a. slight extent and not at the same peripheral rate as the knife moves. The rotation of the stone serves to present a new portion of the abrasive to the knife edge and so prevents undue wear ofthe stone in one locality. Numerous modifications of this construction may be apparent to one skilled' in the art.

'I'he method oi' sharpening a knife and the operations of the above described devices have been fully set forth in the above disclosure. It is apparent that the dierent shapes of stones and the mountings therefor, as well as the mechanisms for rotating the stones, lend themselves to varied uses and provide numerous advantages. Hence, it will also be appreciated that many changes may be made in these constructions and.

shapes of wheels and that the claims are to be interpreted broadly as covering such changes as would be apparent to one skilled in the art.

Having thus described my invention, what I claim as new and protectable by Letters Patent is:

1. A knife sharpening device comprising a support, a spindle rotatably mounted thereon, an abrasive wheel having an veffectivev surface of abrasive grains shaped as a concave conoid generated by an arc of a circle of 1 to 4 inches radius, means connecting the wheel to the spindle, bearings to support the wheel Vagainst the abrading pressure, and means for rotating the wheel at an effective peripheral rate of not over 900 surface feet per minute.

2. A knife sharpening device comprising a support, a spindle rotatably mounted thereon, an abrasive wheel having an effective surface of fine sized abrasive grains shaped as a concave conoid generated by revolving an arc of a circle of 1 to 4 inches radius about'an external axisV arranged close to one end only of the arc and thus forming a body tapering from a narrow end of low abrading characteristics to a wide portion of large diameter, means for mountingthe wheel on the spindle forrotation about said axis, bearings to support'the wheel against the abrading pressure and vmeans for rotating the wheel.

3. A knife sharpening device comprising a support, a spindle rotatably mounted thereon, an abrasive wheel having an eiective surface of abrasive grains shaped as a tapered concave conoid generated by revolving an arc of a circle of 1 to 4 inches radius about anv externalaxis spaced'more Widely from one en d than the other and which is so constructed that theA knife edge to be sharpened may contact with a more rapidly moving surface portion than does the back edge of the blade, said wheel also having a second abrasive surface shaped as an extensive, unob-,

structed circular plane arrangedperpendicular to the axis of the Wheel, means connecting the .wheel to the spindle for rotation about said axis,

4. A knife sharpening device vcomprising an abrasive wheel having an extensive upperlplane circular abrasive surface and a peripheral abrasive surface shaped as a concave conoid developed by revolving an arc of a circle of 1 to 4 inches radius about an external axis, a support, a vertical spindle to rotate the wheel, means including a thrust bearing for mounting the wheel and spindle on the support, means for connecting the wheel to the spindle for revolution about said axis without obstructing the use of either abrasive surface for a knife sharpening operation, and means for rotating the spindle.

5. A knife sharpening device comprising a body having an effective abrasive surface shaped as a concave conoid developed by revolving an' arc of a circle of l to 4 inches radius about an external axis and a second extensive plane abrasive `face on thelarge end thereof which is perpendicular .to said axis, and means for mounting the body for rotation about said axis which does not present non-abrasive material on the plane face thereof capable of interfering with the sharpening action, and said parts being so arranged that a knife may be sharpened on either` face and its bevell determined bysaid radius.

6. A knife sharpening wheel shaped to provide a concave conoid surface developed by revolving an arc of a circle about an external axis, an annular portion of said surface being formed of bonded abrasive grains, and a further annular another abrasive surface shaped as a cylinder and a third abrasive surface providing an extensive plane face, saidwheel being shaped and arranged for rotation about said` axis.

8. A knife sharpening device having an abrasive surface shaped as a concave conoid and a spindle mounting therefor including a friction device which permits rotation of the wheel under restraint when a knife edge is drawn across its lperipheral surface.

CLAYTON L. JENKS. 

